Focus on CME at the University of Calgary Carpal Tunnel Syndrome The non-idiopathic causes of carpal tunnel syndrome (CTS) involve intrinsic and extrinsic conditions responsible for nerve compression. To establish a work-related association, there should be a history of excessive or unusual hand use of a nature known to be associated with CTS prior to the onset of symptoms. By Ron Gorsché, MD, MMedSc (Occupational Health), CCFP arpal tunnel syndrome (CTS) is responsible about CTS and it is among the most controversial C for the most time lost in the workplace, yet of disorders. This article focuses on how recent lit- there is little consensus regarding work as a erature has contributed to the theories of patho- causative factor of the syndrome. Little is known physiology and pathogenesis of CTS, and pro- vides clinicians with a more scientific approach Dr. Gorsché is clinical associate pro- to causative factors and treatment. fessor, departments of family medi- cine and community health sciences, faculty of medicine, University of Historical Perspectives Calgary, and director, Work-Related In 1860, Paget reported the first cases of median Upper Limb Disorders Research nerve compression of the wrist — one case attrib- Unit, Calgary, Alberta. He is also uted the disorder to a tight band wrapped around active staff, High River General the wrist and the other cited complications asso- Hospital, High River, Alberta. ciated with a fractured distal radius.1 In 1941, The Canadian Journal of CME / October 2001 101 Carpal Tunnel Syndrome Woltman first postulated the possibility of nerve toms of CTS. This approach works well for the compression within the carpal tunnel as a cause of clinician attempting to explain the syndrome to a “median neuritis,” after reporting 12 cases associ- patient, but requires further classification for epi- ated with acromegaly.2 demiological study. It also is effective when con- Phalen, who reported his extensive clinical sidering treatment options. experience between 1950 and 1972, supported Although there is no gold standard case defini- active hand use as a factor in symptom aggrava- tion for epidemiological study, to simply use “arm tion, but cast doubt on work as the sole etiology.3 pain” as a definition, as does the Department of Phalen raised one of the primary issues concerning Labor in the United States, grossly overestimates the definition of work-related aspects of CTS. He the prevalence. A combination of median nerve- noted the distinction between factors that aggra- specific symptoms and electrodiagnostic signs vate symptoms of CTS and factors responsible for provides the most accurate diagnostic information the development of the condition. (Table 1).4 To rely solely on positive nerve con- duction studies has a poor predictive value, since, in some populations, as few as 22% of individuals Defining found positive by Nerve Conduction Study (NCS) Carpal Tunnel Syndrome actually had CTS symptoms. After 17 months of follow-up with a matched cohort, this finding did CTS can be defined simply as a complex of symp- not change. Furthermore, these workers were not toms resulting from the compression of the medi- found to be at risk for future development of CTS. an nerve at the carpal tunnel. Median nerve entrap- In the presence of electrodiagnostic data, physi- ment is the pathological process that causes symp- cal findings aside from thenar muscle wasting add Summary Carpal Tunnel Syndrome • CTS occurs as a result of an increase in pressure transmitted to the median nerve within the canal. •Measuring carpal tunnel pressure during various hand and wrist positions allows physicians to determine optimal positioning for splints and in prescribing work restrictions. •To establish a work-related association, there should be a history of excessive or unusual hand use of a nature known to be associated with CTS prior to the onset of symptoms. • The goal of treatment is the resolution of symptoms and preservation of hand function. A significant number of CTS patients will improve with no treatment. This is especially true for those young workers with severe initial impairment. Nonsteroidal anti-inflammatories (NSAIDs), prednisone (1 mg/kg) orally, steroid injection into the carpal tunnel, vitamin B6 (pyridoxine) and vitamin C have all been used in treatment, although not all have been proven efficacious. • Surgical treatment should only be considered in the presence of ongoing symptoms or signs of thenar wasting, together with electrodiagnostic confirmation. • The most successful return-to-work outcomes have occurred when the wrist is not splinted post- operatively and the patient is instructed in a graduated program of early mobilization. 102 The Canadian Journal of CME / October 2001 Carpal Tunnel Syndrome Table 1 The Likelihood of CTS Based on Clinical and EDS Findings* Category Symptoms Electrodiagnostics(EDS) Ordinal Likelihood of CTS Classic/Probable Nocturnal Positive +++ symptoms, tingling, burning or pain in at least 2 digits of 1,2, or 3. Palm pain, wrist pain or radiation proximal to wrist. Classic/Probable As above Negative +/- Possible Tingling, numbness, Positive + + burning or pain in at least 1 of the first 3 digits 1,2, or 3 Unlikely No symptoms in Positive __ digits 1,2,3.4 *In the absence of electrodiagnostic studies, a combination of symptoms and one positive provocative sign, such as Tinels, Phalens, wrist compression test or 3 point discrimination gives the best diagnostic information. *Thenar muscle wasting is the only truly objective physical sign of CTS and increases the likelihood of CTS in all categories. little to the accuracy of diagnosis. All other working population in a Montreal study has been provocative diagnostic tests, such as Tinel’s, calculated to be 0.9 per 1,000 adults.6 In studies of Phalen’s, wrist compression, and two-point dis- specific groups of workers, the incidence in com- crimination, are subjective and, therefore, are not puter users is actually no different than in the gen- sensitive. In the absence of electrodiagnostic test- eral population, whereas in meat packers it is ing, however, adding one positive provocative reported as high as 11 per 100 person years.7,8 physical finding to the case definition is most accu- rate. Anatomy •This fibro-osseous U-shaped canal is made up Prevalence and Incidence of a bony floor and walls and a roof of fibrous The prevalence of CTS in the general population flexor retinaculum. The proximal edge of the has been estimated to be 5% for women and only canal is near the distal wrist crease at the level 0.6% for men.5 The surgical incidence among the of the pisiform carpal bone. The canal then The Canadian Journal of CME / October 2001 103 Carpal Tunnel Syndrome extends distally about 2.5 cm to the level of the hook of hamate. The normal contents of the canal or tunnel include the flexor digitorum profundus and flexor digitorum superficialis tendons of digits II-V, the flexor pollicis longus and the median nerve as shown in Figure 1. •Tendon sheaths cover the tendons within the carpal tunnel. The tendon sheath for the flexor pollicis longus, also called the radial bursa, begins proximal to the carpal tunnel and extends to the base of the distal phalanx of the thumb. The ulnar bursa is larger and covers the superficial and deep tendons of digits II-V. It also begins proximal to the carpal tunnel, extending to the base of the distal phalanx of digit V and to the middle of the metacarpals. • In many individuals, the proximal ends of the lumbrical muscles that originate on the flexor Figure 1. Carpal tunnel anatomy digitorum profundus tendon enter the distal end of the carpal tunnel during flexion.9 At the opposite, or proximal end, of the carpal tunnel, the flexor muscle bellies will pass by the pisi- form carpal bone at the entrance to the canal when the wrist is extended greater than 30 degrees and intra canal pressures would exceed 30 mmHg, if fingers were extended to 0 degrees or flexed greater than 45 degrees.10 • Although the median nerve innervates the thumb, index, middle and one-half of the ring fingers, aberrant or cross-over innervation from the ulnar nerve has been found in 30% of hands. The motor branch of the median nerve to the thumb can exit prior to the flexor retinacu- lum, in the middle, or distal to it. Peripheral Nerve Structure and Function Figure 2. Hand diagram used to localize symptoms to median, ulnar or radial nerve. Median nerve = yellow; The neuron consists of a cell body located in the ulnar nerve = blue; radial nerve = red. anterior horn (motor) or dorsal root ganglia (sen- 104 The Canadian Journal of CME / October 2001 Carpal Tunnel Syndrome Table 2 Effects of Compression on the Peripheral Nerve • Pressures of 80 mmHg (10.7 kPa) interrupts all intraneural blood flow. • Pressures above 30 mmHg (4.0 kPa) inhibit all antegrade and retrograde axonal transport. •When extraneural pressure fluctuates rapidly, the effects on nerve function are associated with the mean value of the pressure waveform. • There is an increased tolerance for high pressures among those with hypertension. The critical extraneural pressure threshold above which nerve function is blocked is 30 mmHg (4.0 kPa) below the diastolic pressure. CTS often manifests itself after treatment for hypertension. • Compression of 30 mmHg (4.0 kPa) led to an elevated intraneurial pressure that persisted for 24 hours. These effects are likely due to the increased vascular permeability of the epineurial and endoneurial vessels producing edema after compression. •A pressure of 30 mmHg applied to the median nerve appears to be the critical threshold for injury. sory) and an axon extending into the periphery, endoneurial space, and the tissue pressure with- and made up of myelinated and non-myelinated in the fascicle is slightly positive.